Products normally used in the production of soiless mixes for greenhouse crop production are often water repellent (hydrophobic) in nature. The hydrophobic surface chemistry of these materials, particularly those from organic sources, is somewhat peculiar and does not relate well to other surfaces. Such components as sphagnum peat moss, hypnum peat moss, reed-sedge peat, composted bark and rockwool which are used in such growing mixes to increase their water holding capacity often become very difficult to wet defeating the purpose for which they were originally intended. The difficulty in wetting increases as the mix dries out normally in storage after preparation or when used to pre-fill pots and flats by the grower and stored for some time before use. This situation presents many problems to the grower as getting the mix evenly wetted is of paramount importance to the healthy growth of the plants or seeds which are grown in the mix. Without water the plants will die.
A possible answer to this problem is to add an appropriate surfactant to the mix to reduce surface tension between the applied water and the hydrophobic mix components. The use of materials currently in commerce is not entirely satisfactory. Relatively high rates of these materials are required to get good wetting properties of the mix and at such rates can be injurious to crop growth. Furthermore, the conventional dry formulations of these materials based on corn cob grits and vermiculite do not work well as the surfactant must first be dissolved from these carriers and bind to the hydrophobic surfaces of the peat, rockwool or bark before they become activated. Consequently, several waterings are normally required before they become active. Furthermore there is an environmental concern as the described compounds contain nonyl-phenol ethoxylates or other mono or di-alkyl phenol ethoxylates. The conjenors of such compounds are known to bioaccumulate in the biosphere with deleterious effects on fresh water crustaceans and their use has been banned in many countries.
The majority of the surfactants currently discovered and developed have been designed to give fast wetting as they are used as cleansers, soaps and detergents. The problem with greenhouse mixes is that fast wetting is not necessarily desirable as they would have to be applied with each watering. What is more desirable is rewetting of the peat or other substances following treatment with a surfactant giving residual activity.
Unfortunately many such surfactants can also have biological activity. They can, in fact, be detrimental to plant growth and many are actually fatal and can act as herbicides. Others have other biological activity and can cause death of insects. Many of these compounds we have previously tested were found to interfere with seedling growth. I have shown earlier that such materials act by disrupting membrane integrity as the hydrophobe bonds to the phospholipid Membrane of the cell wall. Others can act as plant growth regulators and while their use may be beneficial in achieving certain results they cause undesirable effects in greenhouse crop production.
Furthermore, if the selected surfactant is to remain active in the mix beyond the initial watering it is desirable that the hydrophobe of the surfactant bond tightly to the hydrophobic mix component and not leach out when plants are repeatedly watered.
In addition, it is highly desirable that such a surfactant be compatible with fertilizers and other water soluble chemical charge stocks used in preparation of the final horticultural mix.
Although such materials may be applied as a liquid it is also desirable that they may be presented in a dry formulation for ease of application and use by the grower. This creates an additional problem in that most carriers commonly used such as vermiculite, corn cob grits, clay and so forth also absorb the surfactant or tightly bind them to their surfaces making it necessary for the surfactant to first be dissolved from the carrier before it can become active.
Although there are over 4000 surfactants currently in commercial use the discovery of such a surfactant for use in soiless mixes such as root media is therefore not a trivial problem as it must meet certain specific and difficult criteria, namely:
(1) Be compatible with the surface chemistry of peat, rockwool and bark,
(2) Safe for plant growth, particularly seed germination and seedling growth,
(3) Bind tightly to mix components so that it is not leached from the matrix following watering and have residual activity for a full normal cropping season.
(4) Give not only fast initial wetting but also and more importantly rewetting after application to the mix components,
(5) Be compatible with fertilizers and other chemical components and
(6) Have ease of application and be effective in both a liquid and solid formulation.
Surprisingly we have found that certain surfactants belonging to the general class of polyoxyalkylenes meet conditions 1, 2, 3 and 4 and that specific formulations of some members of this class meet conditions 5 and 6. Furthermore, these materials are superior in all six respects to known products used for this utility and which are now commercially available.
Surfactants of this type are described in U.S. Pat. Nos. 4,764,567, 3,086,118, 2,677,700 and 2,674,619. These patents teach us the preparation and use of such materials as surface active agents for use as cleansers and detergents and as wetting agents in the textile, rubber, paper, lacquer, leather and like industries but no mention is made of their use in soils or soiless horticultural media nor in their interaction with living organisms nor for general applications in the Agricultural or Horticultural industries. Furthermore, despite the age of these patents their use for such utilities is unknown.
To date, no correlation has been shown between a chemical structure of a particular class of surfactants and its phytotoxicity (in this case crop safety) to seed germination and plant growth. Indeed the converse is true with most surfactants known to be injurious to plants. This is not surprising as surfactants in general because of their solubilizing and dispersing nature will dissolve plant cuticles, interfere with plant membranes and generally disrupt membrane integrity in tender plant tissue as their hydrophobes will bond to such lipophyllic organs found in plants such as emerging roots, root hairs, radicles and hypocotyls. The discovery of such surfactants which will maintain good wetting properties in the surrounding media without interfering with plant growth is therefore surprising and unusual.